Generating flat landmasses with bounds

I am wondering how I can select gameObjects in groups randomly so they form landmasses. Since I already have them laid out in the hierarchy, all I really need is to figure out how to randomly select these gameObjects in groups shaped like landmasses, since it would be unnecessary to create multiple different maps. There are 2500 gameObjects that are children of one gameObject. I don't really know if this question is too vague. Please tell me if it is so, I'll be glad to clarify.